Gas Exchange in Humans

Question 1

What happens as you breathe in?

Answer 1

Air enters the trachea. The trachea splits into two bronchi - one bronchus leading to each lung. The bronchus branches off into bronchioles. The bronchioles end in alveoli. The ribcage, intercostal muscles and diaphragm all work together to move air in and out

Question 2

What does ventilation consist of?

Answer 2

Inspiration and expiration

Question 3

Explain inspiration

Answer 3

1. The external intercostal and diaphragm muscles contract
2. Ribcage moves upward and outwards, the diaphragm flattens, increasing the vol of the thoracic cavity
3. This causes lung pressure to decrease
4. Air flows down a pressure gradient down the trachea and into the lungs

Question 4

Explain expiration

Answer 4

1. The external intercostal muscles and diaphragm relax
2. Ribcage moves downwards and inwards, diaphragm curves again
3. Vol of thoracic cavity decreases, causing air pressure to increase
4. Air is forced down a pressure gradient out of the lungs

Question 5

What happens during forced expiration?

Answer 5

External intercostal muscles relax, internal intercostal muscles contract, pulling ribcage further down and in. Movement of these two sets of muscles is antagonistic

Question 6

What is an alveolus made from?

Answer 6

A single layer of thin, flat cells called alveolar epithelium

Question 7

How do gases move across the alveoli?

Answer 7

O2 diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into the haemoglobin in the blood. CO2 diffuses into the alveoli from the blood, and is breathed out

Question 8

How are the alveoli adapted for gas exchange?

Answer 8

1. A thin exchange surface
2. A large surface area
3. Steep conc gradient of O2 and CO2 maintains by flow of blood and ventilation